1. Field of the Invention
The present invention relates to a surface position detection apparatus for detecting a position of a surface to be detected.
2. Related Background Art
In a semiconductor exposure apparatus for transferring a circuit pattern formed on a reticle onto a wafer through a projection lens, the focal depth of the projection lens is relatively small, and a three-dimensional pattern is often locally present on the wafer. For this reason, a defocused state with respect to the projection lens must be compensated for depending on each exposure region on the wafer. As a detection apparatus for detecting the position of the projection lens in the optical axis direction in this case, for example, U.S. Pat. No. 4,687,322 discloses an oblique incident type auto-focus sensor for obliquely projecting a slit image onto a surface to be detected of, e.g., a wafer. In this example, when the surface to be detected is vertically shifted, the position of the slit on the surface to be detected is shifted in a direction perpendicular to the optical axis of an oblique incident optical system. Thus, the position of the surface to be detected in the optical axis direction can be detected by measuring this shift amount.
For example, Japanese Patent Application Laid-Open No. 1-253603 discloses a surface position detection apparatus, which obliquely radiates three or more light beams onto a surface to be detected through a projection lens system having a common portion in order to simultaneously measure the positions of a plurality of points on the surface to be detected. In this example, a compensation optical system is built in, so that a plane including light sources of the three or more light beams is perpendicular to the optical axis of the common projection lens.
However, in the conventional detection apparatus, it is impossible to simultaneously detect vertical positions in a region over a wide range on a surface to be detected.
In this case, according to the apparatus disclosed in Japanese Patent Application Laid-Open No. 1-253603, when the number of obliquely incident light beams is increased to increase the density, the vertical positions in a region over a wide range can be detected. However, this makes the overall optical system including the compensation optical system complicated, and adjacent light beams undesirably have some interval therebetween.
In recent years, along with an increase in integration degree of LSIs, it is demanded to transfer micropatterns onto exposure regions (shot regions) on a wafer. In order to meet this demand, the numerical aperture (N.A.) of a projection lens for transferring an image of a circuit pattern onto a wafer is increased. For this reason, since the focal depth of the projection lens becomes small, it is demanded to precisely and reliably locate each exposure region within the focal depth of the projection lens.
Furthermore, when a plurality of LSI chips are simultaneously exposed, or when the size of an LSI chip to be exposed (the size of an exposure region) is to be changed, light for position detection cannot be radiated on a proper position on a surface to be detected in this state. In order to perform precise position detection, a position to be irradiated with light on an exposure region must be changed. In order to perform precise position detection with the conventional detection apparatus under these circumstances, a plurality of positions of each exposure region on the wafer must be detected. However, this makes an optical system complicated.
A stage which carries the wafer may be sequentially moved to a required detection position by projecting slit light from the detection apparatus onto the required detection position. However, the time required for position detection is prolonged, and the throughput is decreased.